The advanced properties achieved by modern ceramic matrix composite (CMC) structures depend critically on the surface condition of reinforcement materials used in the manufacturing process. Contamination of reinforcement surfaces can result in brittle phases, low melting point eutectics, or foreign compounds at the critical interface between the reinforcement material and the ceramic matrix, which can compromise the composite"s strength and/or chemical resistance. Such effects have been attributed to cumulative water vapor contamination of silicon carbide (SiC) fiber reinforcement fabrics used in SiC/SiC CMCs, such as those used in modern high temperature aircraft propulsion systems. Creare proposes to develop a passive sensor of cumulative humidity exposure to assist manufacturers with monitoring water vapor contamination of CMC reinforcement materials. The low-cost sensors will travel with individual ceramic fiber fabric rolls or containers of humidity sensitive material during shipping, storage, and handling, and can be read nondestructively by a handheld sensor reader whenever the humidity exposure history needs to be checked. In this Phase I project, Creare will develop prototype sensor components and demonstrate their basic functionality for measuring cumulative humidity exposure. In a future Phase II program, we will finalize the sensor designs, fabricate prototype sensors, and demonstrate them in laboratory experiments.